The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Vehicles typically include an engine system that produces drive torque for driving one or more wheels. Hybrid engine systems include an internal combustion engine used alone or in combination with an electric motor to produce drive torque. Internal combustion engines combust an air and fuel mixture (A/F mixture) within cylinders to drive a crankshaft via pistons located in the cylinders, which produces drive torque. Air and fuel flow into and out of the cylinders may be controlled by valves that selectively open to allow flow into and/or out of the cylinders and close to trap air and fuel within the cylinders. Operation of the valves is controlled by a valvetrain.
By-products of combustion are exhausted from the engine via an exhaust system. The exhaust system may include a catalytic converter that reduces a concentration of certain by-products present in the exhaust, such as nitrogen oxides (NOX), carbon monoxide (CO), unburned hydrocarbons (HC), sulfur oxides (SOX), and other compounds.
Catalytic converters include a catalyst that facilitates chemical reactions that reduce the concentration of the by-products. For example, three-way catalytic converters include a catalyst that converts NOX to nitrogen and oxygen, CO to carbon dioxide (CO2), and HC to CO2 and water (H2O). Catalysts, in order to function properly, must be operated at temperatures above what may be referred to as a light off temperature. After prolonged idle periods, the temperature of the catalyst may be below the light off temperature.